WordPress v2.7 uses an older version of Magpie RSS (v0.51) which has some bugs that may prevent your RSS feed displaying in your WordPress blog/theme.

I happen to use KB Advanced RSS Widget, on the IrelandOffline site, but I believe most RSS widgets/plugins for WordPress use.
The issue in my case, was a a simple apostrophe, on a vBulletin forum, being converted to a fancy apostrophe (character \x92).

The most recent Magpie RSS version (v0.72 at time of writing) handles this OK. So to update your WordPress installation to use this most recent release of Magpie RSS, do the following: